RU2431049C2 - Catalyst with improved parameters of operation beginning - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: catalyst for cleaning of waste gases of internal combustion engines contains honeycomb element consisting of plain and corrugated metal sheets with inlet end surface and outlet end surface for waste gases; at that, metal sheets are provided with holes for reduction of their heat capacity, and catalyst mass is applied to metal sheets; at that, holes of metal sheets are filled with catalyst mass, and surface area of all the holes is 5 to 80% of the surface area of metal sheets. Also, use of catalyst for cleaning of waste gases of internal combustion engine is described.

EFFECT: reduction of heat capacity and heat conductivity of catalyst.

12 cl, 7 dwg

Description

The present invention relates to metal honeycomb elements as carriers for coating a catalyst material for treating exhaust gases of internal combustion engines.

On the one hand, a large geometric surface is required from the honeycomb elements for coating, and on the other hand, a low heat capacity is desirable so that the honeycomb element quickly heats up to the operating temperature of the catalyst. Along with this, the honeycomb elements must have sufficient mechanical stability in order to withstand the mechanical stresses arising from the pulsating gas flow and vibration of the engine and vehicle. In addition, the material of the honeycomb elements must be resistant to the corrosive atmosphere of exhaust gases at high temperatures.

The catalytic coating of the finished catalyst consists of finely dispersed heat-resistant metal oxides, on the surface of which the active metals of the platinum group are deposited by catalytic method. Suitable are, for example, the following metal oxides: alumina, titanium oxide, silica, ceria, zirconia, zeolite and mixtures thereof or mixed oxides, as well as stabilizers such as lanthanum oxide and barium oxide. For applying these materials to a honeycomb cell, powdered substances are converted, for example, into an aqueous suspension. Subsequently, this coating suspension is deposited onto the honeycomb elements in a known manner, dried and hardened by calcination.

Cell elements may have a different structure. Already at a fairly early time, cell elements twisted in a spiral were used. They consist of one sheet of smooth and one sheet of corrugated metal sheet, which are superimposed on each other, and then spirally twisted and placed in a casing. Both metal sheets form channels through which exhaust gases exit and can intensely come into contact with the catalytic coating.

In another constructive embodiment, the honeycomb element is made of numerous alternately arranged sheets of smooth and corrugated or corrugated metal of varying degrees, the metal sheets first forming one or more feet that are intertwined. The ends of the metal sheets remain outside and can be connected to the casing. Thus, there are numerous connections between the metal sheets and the casing, which increase the mechanical strength of the honeycomb element.

As the material for the metal sheets, steel alloys are preferably used, which, for example, are commercially available under the trade name FeCrAlloy®. This is an alloy of iron-chromium-aluminum. The thickness of the metal sheets is usually from 20 to 80 microns, preferably 50 microns.

It has long been known to supply metal sheets with holes and grooves in order to influence the flow in the channels and / or to achieve transverse mixing between the individual flow channels. It is also known to use cut along metal sheets to create metal honeycomb elements. US 5599509, for example, proposes to make slots in the area of the entrance to the cell element across the direction of the exhaust gas flow in order to purposefully reduce the heat capacity of the cell element in this region.

By reducing the thermal conductivity and heat capacity in the front part, the deposited catalyst coating quickly reaches its reaction temperature, and thereby also a better exchange, for example, carbon monoxide and hydrocarbons. However, the improvement in exchange clearly depends on the percentage of the slit surface of the metal sheets. Exchange improves only when the area of the slotted surfaces takes from 20 to 50%. Above the limit of 50%, the hydrocarbon exchange decreases again, since the available catalyst mass decreases with an increase in the slit surface with a constant thickness of the catalyst layer. Therefore, an improvement in metabolism can be observed only in the warm-up phase. After the warm-up phase, a decreased catalyst mass leads to a deterioration in the metabolism of harmful substances in the exhaust gases. In addition, such a catalyst has a low resistance to aging due to the low catalyst mass. Moreover, the system of openings on the metal sheets increases the dynamic pressure of the catalyst, since turbulences form at the openings. If they wanted to apply the same catalyst mass on such a catalyst carrier as on a carrier with the same geometry without holes, the thickness of the catalyst layer would necessarily increase, and thereby also the dynamic pressure of the catalyst.

DE 10314085 A1 also describes metal honeycomb elements consisting of at least partially perforated metal sheets. The purpose of the holes is to make it possible to cross-mix the flow of exhaust gases from various flow channels. Therefore, when applying the coating, pay attention to the fact that the holes are not closed by the coating suspension. For this reason, the honeycomb elements are coated in a vibration device that carries out relative motion between the coating suspension and its carrier, and thereby prevents clogging of the holes.

US 5821194 describes a metal honeycomb element of sheets of smooth and corrugated metal. To improve the adhesion of the pre-coating mass, the metal sheets are provided with numerous holes into which the pre-coating mass penetrates during the coating process and engages the metal sheets and the coating mass mechanically. For this, the diameter of the holes is approximately half the thickness of the metal sheets and thereby ranges from 25 to 35 microns. The holes are located at a distance of about 1 mm from each other.

The present invention should eliminate the disadvantages of the prior art drawbacks of metal surfaces. The objective of the invention is the compensation of suitable measures of surface loss of the carrier, due to the area of the holes of the metal sheets.

This problem is solved by using a catalyst for cleaning exhaust gases of internal combustion engines, which contains a honeycomb element made of sheets of smooth and corrugated metal with an input end surface and an output end surface for exhaust gases, the metal sheets provided with openings and / or slots to reduce their heat capacity, and a catalyst mass is applied to the metal sheets. The catalyst is characterized in that the openings and / or slots of the metal sheets are, as far as possible, completely filled with the catalyst mass, and the area of the openings of all the holes together makes up 5 to 80% of the total area of the metal sheet.

In contrast to US 5,599,509, the openings and slots on the metal sheets are filled according to the present invention with a catalyst mass. Filling with a catalyst mass or preliminary coating is carried out immediately before the coating process; no additional workflows are required. If the same amount of catalyst mass is used as in the case of carriers of the same geometry without holes, the heat capacity is reduced by the percentage of holes in the metal sheets. The physical characteristics in table 1 can serve to evaluate these effects.

Table 1 Comparative physical characteristics of FeCrAlloy alloy and aluminum oxide catalyst layer Properties FeCrAlloy Catalyst layer Density, g / dm ³ 7.28 1.2-1.6 Part, heat capacity, J / (kg · K) 480 750-950 Thermal conductivity, W / (m · K) 16 1.4

According to the invention, the advantage is that the holes in the metal sheets do not lead to a decrease in the catalyst mass. As a result, the proposed catalyst, by reducing the heat capacity of the carrier, very quickly reaches its reaction temperature and then develops the full activity of the unabridged catalyst surface. In addition, the proposed catalyst due to the high concentration of the filling of the catalyst mass has increased resistance to aging compared with traditional catalysts with holes.

Of course, the same filling concentration could also be achieved according to the prior art without capping the openings on the honeycomb. However, then the coating thickness would inevitably be significantly larger and thereby would lead to increased flow resistance in the catalyst.

For the manufacture of the catalyst according to the invention, the properties of the coating slurry must correspond to the size of the holes in order to ensure that, with the catalyst mass, all holes are completely filled. Liquid flowing coating suspensions may clog only small openings; thick flowing coating suspensions, in contrast, also cover larger openings.

The person skilled in the art can easily determine the optimal conditions by conducting several preliminary tests.

The shape of the holes may not be round. The area of holes covered by the coating suspension depends on the shape of the holes and the properties of the coating suspension. In general, the area of individual holes may be from 0.1 to 25 mm ² . In the case of round holes, the area of the holes is 0.1 to 1 mm ² ; in the case of oblong holes, their area, on the contrary, can be from 0.25 to 25, preferably from 0.25 to 5 mm ² . Therefore, the holes within the mentioned restrictions can be round, elliptical, oval, square, rectangular, slit-like or polygonal.

If the above list of characteristics of the coating suspension and the overall dimensions of the hole is observed, then for the direct coating process, known methods of coating by dipping, dousing, suction or injection can be applied. When removing excess coating slurry by blowing with compressed air, it should be noted, however, that during this process, openings plugged with a moist catalyst mass do not open again.

After the coating suspension has dried, it is calcined at a temperature in the range of about 300 to 600 ° C. Then the holes are corked with a strong layer of catalyst mass, which withstands the harsh operating conditions in the exhaust gas path of the internal combustion engine.

Thus, as in the case of a honeycomb element without holes, depending on the desired coating thickness, a coating concentration of 50 to 400 grams per liter of volume of the honeycomb element can be achieved. If it is necessary to achieve the same concentration of the coating without clogging the holes, it would be appropriate to increase the thickness of the coating on the metal sheets accordingly.

For the production of the honeycomb element, preferably all metal sheets, both smooth and corrugated, in perforated form are used. The advantages of the invention, however, are manifested - albeit in a weakened form - also if, for example, sheets of only smooth or only corrugated metal in perforated form are used.

In addition, it may be appropriate to limit the location of the holes only to a specific area of the honeycomb element. An advantage is, for example, the placement of holes only in the region of the oncoming flow of the honeycomb element.

The area of all openings in combination with respect to the total area A of the metal sheets in the area with the presence of openings determines an achievable decrease in heat capacity. According to the invention, the area of all openings with respect to the total area in the perforated region is from 5 to 80%. With an area of more than 80%, the hole system degrades the cell strength too much. Preferably, the proportion of holes is from 5 to 65, in particular from 20 to 65%.

In addition to the holes, the metal sheets may also have grooves and recesses if it is necessary to create a swirl of the exhaust gas flow to improve contact with the catalytic coating.

The use of metal sheets of the so-called expanded metal sheet for forming a cellular element proved particularly favorable. An expanded metal sheet is a metal sheet with openings, the so-called cells, which are formed by offset notches while simultaneously stretching without loss of material horizontally with respect to the notches. The expanded metal has a lattice structure with rhomboid or slit-shaped cells. The cells consist of jumpers and holes bounded by them. Crossing points of jumpers are called nodal points. The cell size is determined by the length and width of the cell. The cell length is the distance from the middle of the nodal points to the middle of the nodal points in the direction of a long diagonal. The cell width is also determined accordingly. Another characteristic of expanded metal is the width of their lintels.

In the manufacture of an expanded metal sheet from a metal sheet, the width of the metal sheet perpendicular to the direction of drawing remains unchanged, since the bridges are stretched during die-cutting and the sheet not yet stamped in front of them resists deformation. In this case, a corrugated, plastically structured surface of the expanded metal sheet is formed. In case a smooth surface is required, the expanded metal sheet can be rolled with rollers after stretching. Expanded metal sheet can be made with a free cross-sectional area of from 4 to about 90%.

For the proposed catalyst, smooth or corrugated metal sheets, or both types of sheets may consist of expanded metal sheet. The cell length is preferably from 0.5 to 5 mm with a stretch ratio of from 5 to 80, preferably from 10 to 50%. Good results were achieved with expanded metal with 30% stretch. A 30% stretch means that the expanded metal sheet after manufacture has a length equal to 1.3 of the length of the original sheet. Such a sheet also has a free hole area of about 23% and a mass reduced by this percentage relative to a conventional sheet of the same length.

The corrugated surface of the expanded metal sheet has a beneficial effect on the catalytic effect of the finished catalyst, since this causes turbulence of the exhaust gases in the flow channels of the catalyst, and thereby improves contact with the catalyst coating. However, for this reason, the exhaust backpressure also increases. If this is undesirable, expanded metal sheets may be aligned with rollers before the catalyst body is formed therefrom.

The catalysts according to the invention are used for purification of exhaust gases of internal combustion engines. In this case, the catalytic coating can meet the special requirements of the composition of the exhaust gases. The coating may comprise an oxidation catalyst, a three-component catalyst, a nitric oxide storage catalyst, and a selective catalyst reduction catalyst. The catalyst proposed according to the invention can be used in vehicles with internal combustion engines with forced ignition of the working mixture or with a diesel engine, as well as a catalyst located next to the engine for starting and warming up the engine, or as a catalyst located under the underbody. A catalyst is particularly preferred for the exhaust gas treatment of motorized two-wheeled vehicles and floating vehicles.

A further interpretation of the invention are figures 1 to 7. The drawings show:

Figure 1-4: examples of perforated metal sheets with various shapes of holes and their content,

Figure 5: an example of improved start-up parameters of the catalyst,

6: photographic images used for forming a honeycomb element expanded metal sheet with a degree of stretching of 30%,

a) without coating,

b) after applying a catalytic coating.

7: a comparative measurement of the exhaust gas output in the European motorcycle test cycle with a conventional honeycomb element consisting of metal sheets without holes and a honeycomb element according to the invention with metal sheets made of expanded metal sheet.

In FIG. 1 through 5 show several examples of possible hole systems of metal sheets in the corresponding scale of the image at double magnification.

Figures 1 and 2 show hole systems of rounded holes with a diameter of 0.8 mm or more. The hole systems of FIGS. 1 and 2 differ from each other by the distance of the holes from each other and, thus, by a different percentage of the area per hole. According to figure 1, the area of the holes is 50% of the perforated area of the sheet, while according to the system of holes in figure 2, the area of the holes is only 25%.

Figures 3 and 4 show a system of holes with longitudinal holes of various sizes and with different percentages of the area of the holes.

Modeling Calculations

To prove the advantages of the catalyst according to the invention, simulation calculations were performed. As a basis for the simulation, measurements were made of the exhaust gas composition, that is, the concentration of harmful substances and the temperature of the exhaust gas, of a motorcycle with a four-stroke engine with a volume of 1200 cm ³ according to the EU3 test cycle depending on the time of the test.

To calculate the reaction of harmful substances, two metal honeycomb cells with a cell density of 360 cm ^-2 , a diameter of 90 mm and a length of 74.5 mm were taken. Metal sheets made of FeCrAlloy alloy had a density of 50 μm. When conducting a comparative calculation, it was assumed that the honeycomb element consists of metal sheets without holes, while for the calculation of the example, it was assumed that the honeycomb element has perforated metal sheets with a hole area of 50%. As a catalyst coating, we used a three-component catalyst containing platinum, palladium and rhodium, with the same concentration of the noble metal in both cases equal to 1.48 g / l of the volume of the honeycomb element.

The measurement results and calculations are presented in figure 5 for the first 200 seconds of the EU3 cycle. ″ V ″ denotes a motorcycle speed diagram in accordance with the test cycle. T1 corresponds to the measured dynamics of the temperature of the exhaust gases before entering the catalyst.

Curve T2 in FIG. 5 shows the calculated temperature dynamics behind the compared catalyst without holes, while curve T3 shows the temperature dynamics behind the perforated catalyst of the example. You can clearly recognize that due to the presence of a system of holes, the example catalyst heats up much faster. Thus, the catalyst with holes reaches a temperature of 250 ° C at Δt = 13 s faster than the comparative catalyst.

Example 1: Comparative Catalyst (Catalyst A):

A round cylindrical metal honeycomb element made of metal foil sheets without holes 0.05 mm thick, 90 mm in diameter, 74.5 mm long and 200 cm ^-2 cell density was coated with a traditional three-component catalyst containing platinum, palladium and rhodium, with a concentration of noble metal 1 , 55 g / l of the cell element volume.

Example 2: The catalyst according to the invention (catalyst B)

To compare the catalytic properties, another metal-supported catalyst was manufactured with the same overall dimensions, foil thickness, and cell density as the comparative catalyst. Instead of a metal foil without holes, however, an expanded metal sheet with a degree of extrusion of 30% and a cell length of 0.6, a cell width of 0.5, and a bridge width of 0.18 mm was used. The metal support was coated with the same ternary catalyst of the same concentration as the comparative catalyst.

6 a) shows a photograph of the structure of the used expanded metal sheet before applying the catalytic coating. On figb) shows the corresponding picture after applying the catalytic coating. It can be clearly recognized that the openings of the cells of the expanded metal sheet are completely filled with the catalyst mass. The catalyst mass adhered perfectly to the expanded metal sheet, and peeling did not occur also when compressed air was supplied and tapped.

Dynamic Pressure Measurements:

The dynamic pressure of both metal supported catalysts was measured before and after the catalytic coating was applied at a mass flow of 300 Nm ³ / h (Nm ³ = standard m ³ ). The results are presented in the following table 2.

table 2 Dynamic Pressure Measurement Results Catalyst Dynamic pressure in mbar at 300 Nm ³ / h before cover after coating Increase [%] BUT 5.9 9,4 58 AT 8.2 10.1 22

The proposed catalyst carrier B without coating, due to its three-dimensional structure, has a significantly higher dynamic pressure than a metal carrier with an unperforated metal foil.

After applying the catalyst layer, the dynamic pressure of the compared catalyst rises by 58% from 5.9 to 9.4 mbar. When using a catalyst carrier made of foil made of expanded metal, the dynamic pressure after coating increases only by 22% from 8.2 to 10.1 mbar. A striking result is observed here: due to the filling of the cells of the expanded metal sheet with the catalyst mass, the difference in dynamic pressure between the two catalysts can be neglected in comparison with the increase in the dynamic pressure between the uncoated and coated catalyst carriers.

Exhaust emission measurement in the European motorcycle test cycle:

Catalysts A and B were measured on a motorcycle for their exhaust emissions during the European motorcycle test cycle. 7 shows the total measured values obtained during the tests, on the emissions of CO, PC and NOx of both catalysts depending on the duration of the run. 7 also shows the speed of the motorcycle. The emission curves of coal oxide and hydrocarbon for the proposed catalyst B are significantly lower than the curves of comparative catalyst A. The difference in emissions between the two catalysts is due to the cold start stage, lasting the first 100 seconds, and has a shorter start time due to its lower thermal mass. After passing through the cold start stage, both catalysts convert harmful substances equally well, since they are coated with the same amount of catalyst mass. As a result of this, the emission curves after passing through the cold start stage are parallel to each other.

Table 3 shows the results of phase-by-phase measurements for harmful substances during this test.

Table 3 Phase Measurement Results of the European Motorcycle Test Cycle. Catalyst Phase Results With THS3 *) NOx CO2 BUT g / test 7,008 2,990 1,111 1764,865 g / km 0.5673 0.234 0,087 138,204 AT g / test 5,673 2,043 0.895 1751,660 g / km 0.444 0.160 0,070 137,256 *) THC3: total hydrocarbon calculated as C3.

The results of table 3 show that the proposed catalyst B in comparison with the compared catalyst has a reduced emission of nitric oxide - by 19%, the emission of THC3 - by 31% and the emission of nitrogen oxides - by 19%.

Claims (12)

1. A catalyst for treating exhaust gases of internal combustion engines, comprising a honeycomb element made of smooth and corrugated metal sheets with an inlet end surface and an outlet end surface for exhaust gases, the metal sheets having openings to reduce their heat capacity, and a catalyst mass is deposited on the metal sheets, characterized in that the holes of the metal sheets are filled with a catalyst mass, and the area of the holes of all the holes in the aggregate is from 5 to 80% p the ribs of metal sheets. 2. The catalyst according to claim 2, characterized in that the holes have a round, elliptical, oval, square, rectangular, slit-like or polygonal cross section. 3. The catalyst according to claim 2, characterized in that the holes have an area of from 0.1 mm ² and 25 mm ² . 4. The catalyst according to claim 3, characterized in that the holes are applied to the entire surface of the metal sheets or to a part thereof. 5. The catalyst according to claim 1, characterized in that the smooth or corrugated metal sheets or both types of metal sheets are made of expanded metal, the expanded metal sheet having a cell length from the middle of the node to the middle of the node from 0.5 to 5 mm . 6. The catalyst according to claim 5, characterized in that the degree of stretching of the expanded metal sheet is selected from the interval between 5 and 80%. 7. The catalyst according to claim 6, characterized in that after manufacturing the expanded metal sheet is rolled. 8. The catalyst according to any one of claims 5 to 7, characterized in that the cells of the expanded metal sheet are deposited on the entire surface of the expanded metal sheet or in part thereof. 9. The catalyst according to claim 1, characterized in that it has a loading of the catalyst mass with a concentration of from 50 to 400 g / l of the volume of the honeycomb element. 10. The use of the catalyst according to any one of the preceding paragraphs for the purification of exhaust gases of internal combustion engines. 11. The use of claim 10, characterized in that the catalyst is used on vehicles as a catalyst for starting and warming up the engine or as a catalyst located under the underbody. 12. The use of claim 10, characterized in that the catalyst is used for purification of exhaust gases of motorized two-wheeled vehicles or motorized floating vehicles.

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